Overview
ISO 20596-2:2021 - "Water quality - Determination of cyclic volatile methylsiloxanes in water - Part 2" specifies a validated laboratory method to measure cyclic volatile methylsiloxanes (cVMS) in environmental waters. The procedure uses low density polyethylene (LDPE) as a preservative, followed by liquid–liquid extraction into hexane containing 13C‑labeled cVMS internal standards, and analysis by gas chromatography–mass spectrometry (GC‑MS). Target analytes are D4, D5 and D6 (octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane). The method covers concentrations from 0.1 µg/L to 250 µg/L, with potential for lower detection in well‑controlled labs.
Key topics and technical requirements
- Preservation and sampling: LDPE is used to limit volatilization and adsorption losses during transport and storage; follow general water sampling guidance (ISO 5667 series).
- Extraction: Liquid‑liquid extraction into hexane recovers dissolved and sorbed cVMS fractions; hexane must be verified free of cVMS.
- Internal standards: Use 13C‑labelled, chemically identical cVMS as internal standards added via the extraction solvent to minimize calibration bias.
- Instrumental analysis: Separation and quantitation by GC‑MS; Annex A provides recommended GC‑MS conditions.
- Interferences & contamination control: Avoid silicone-containing consumables and personal care products during sampling and analysis. Use non‑polydimethylsiloxane (non‑PDMS) GC columns for sub‑ppb work, silicone‑free or PTFE‑coated vial septa, and consider inlet septum alternatives to reduce background.
- Quality assurance: Includes blanks, spikes and QC samples (examples in Annex C); method detection limits, limits of quantification and performance data are discussed in Annexes B and D.
- Calibration & calculations: Preparation of multi‑level calibration stocks and use of isotopic internal standards for concentration calculation and quality control.
Applications and users
- Environmental monitoring: Routine surveillance of rivers, streams and wastewater (influent/effluent) for cVMS contamination.
- Regulatory compliance: Laboratories supporting water quality regulations, permitting and environmental impact assessments.
- Research and risk assessment: Academic and industrial studies on fate, transport and exposure to siloxanes.
- Typical users: environmental analytical laboratories, water authorities, consultants, and researchers requiring reproducible, traceable GC‑MS measurement of cVMS.
Related standards
- ISO 3696 - Water for analytical laboratory use
- ISO 5667 series - Water sampling guidance (Parts 4, 6, 10, 14)
- ISO 8466-1 - Calibration and evaluation of analytical methods
- ISO/TS 13530 - Guidance on analytical quality control for chemical water analysis
Keywords: ISO 20596-2:2021, cVMS, cyclic volatile methylsiloxanes, GC‑MS, liquid‑liquid extraction, LDPE preservative, 13C internal standards, water quality, environmental monitoring.